Equipment feeders

[Chrism308]

When sizing feeders from a breaker to a busway, NEC 110.14 (C)(1) says use 310.15(B)(16) as modified by 310.15(B)(7). Using that table, 2000a feed at 75C would be (6) sets of 600 kcmil AL (not calc VD).
But if installing on vented cable tray, how do you interpret the code?
NEC 392.80 (2)(a) notes single conductors in tray shall not exceed 75% allowable ampacities in table 310.15(B)(17) which is table for free air.
NEC 392.80 (2)(d) notes if conductors are in triangular configuration with required spacing on messenger 310.15(B) which leads to 310.15(B)(20) cables on messenger. This case (6) sets of 600 kcmil AL would be 2640A
If you size based on 310.15(B)(16) only, there is no consideration for ventilation on cable tray.

 

[Little Bill]

Bump

 

[texie]

When sizing feeders from a breaker to a busway, NEC 110.14 (C)(1) says use 310.15(B)(16) as modified by 310.15(B)(7). Using that table, 2000a feed at 75C would be (6) sets of 600 kcmil AL (not calc VD).
But if installing on vented cable tray, how do you interpret the code?
NEC 392.80 (2)(a) notes single conductors in tray shall not exceed 75% allowable ampacities in table 310.15(B)(17) which is table for free air.
NEC 392.80 (2)(d) notes if conductors are in triangular configuration with required spacing on messenger 310.15(B) which leads to 310.15(B)(20) cables on messenger. This case (6) sets of 600 kcmil AL would be 2640A
If you size based on 310.15(B)(16) only, there is no consideration for ventilation on cable tray.

You are limited to 310.15(B)(16) @75 degree because that is all the breaker is rated for. And likely your bus connection is also limited to 75 degree.

 

[Chrism308]

You are limited to 310.15(B)(16) @75 degree because that is all the breaker is rated for. And likely your bus connection is also limited to 75 degree.

I understand on the rating. The tables for free air and cable tray have 75c rating ampacities listed. Looks like the table for vented cable tray can be used instead of 310.15(B)(16) if conductors are ran on vented cable tray with required spacing in conditioned spaces.